So far, 5-Hour Energy maker Living Essentials LLC has received 92 reports from people who fell ill after using the product. Since the product is sold as a nutritional supplement, the company is required to relay such reports to the FDA.

The reports themselves do not prove that 5-Hour Energy had anything to do with any of the deaths or illnesses.

"It is important to note that, while those who voluntarily report an illness or injury ... typically identify the product that they assume caused the injury or illness, FDA as a scientific public health agency must carefully investigate and evaluate all possible causes before deciding whether the product actually caused the medical problem," the FDA said in a statement.

5-Hour Energy shots are small caffeinated drinks. The product does not contain any herbal stimulants.

Energy Product Investigations

Recently, the FDA revealed that it is investigating five deaths linked to Monster Energy, another "energy" product. This came on the heels of a government report of a10-fold increase in people who need emergency medical care after guzzling energy products.

Even if 5-Hour Energy shots did cause the injuries, it would be taken off the market only if the injuries resulted from proper use of the product as stated on its label.

In a statement, Living Essentials says it takes these injury reports "very seriously." The company says 5-Hour Energy is safe when used as directed by "hardworking adults who need an extra boost of energy."

The 5-Hour Energy label and the product's web site spell out proper use:

Drink no more than two bottles of 5-Hour Energy a day, spaced several hours apart.

People trying 5-Hour Energy for the first time should try half a bottle and wait 10 minutes before drinking the rest.

People sensitive to caffeine should talk to their doctor before using it.

Throw out any unused product within 72 hours of opening the bottle.

The FDA offers additional advice. In its statement, the agency warns that:

5-Hour Energy and other energy shots or beverages are not alternatives to rest or sleep.

Caffeine and other stimulants may make an unrested person feel more alert and awake, but judgment and reaction time still may be "severely impaired."

Consult a health care provider before using these products to make sure you do not have a medical condition that might get worse if you take them.

Caffeine Levels

Caffeine is the main active ingredient in 5-Hour Energy. Living Essentials says it contains "about as much caffeine as a cup of the leading premium coffee."

A recent test by Consumer Reports found that 5-Hour Energy contains 215 milligrams of caffeine per serving.

An 8-ounce cup of coffee has about 100 milligrams of caffeine, although that varies according to how the coffee is brewed. For example, Consumer Reports finds that 8 ounces of Starbucks coffee has 165 milligrams of caffeine.

According to Consumer Reports, safe limits of caffeine are up to 400 milligrams per day for healthy adults, 200 milligrams a day for pregnant women, and up to 45 or 85 milligrams per day for children, depending on weight.